Adhesion (from Latin adhaesio - sticking) is the adhesion of the surfaces of two dissimilar solid or liquid bodies. Adhesion is due to the same reasons as adsorption. Adhesion is quantitatively characterized by the specific work spent on separating bodies. This work is calculated per unit area of the contacting surfaces and depends on how they are separated: by shear along the interface or by separation in a direction perpendicular to the surface. Adhesion sometimes turns out to be greater than cohesion, which characterizes the adhesion force of particles inside a given body. In this case, the rupture occurs cohesively - inside the least strong of the contacting bodies. The adhesion of solids to an uneven surface is usually low, since they actually come into contact only with individual protruding sections of their surfaces. The adhesion of a liquid and a solid and two immiscible liquids reaches an extremely high value due to complete contact over the entire contact area. When a solid is coated with a polymer in a fluid state, the latter penetrates into the recesses and pores. Once the polymer has cured, a bond occurs, sometimes called mechanical adhesion. In this case, in order to tear off the polymer film, it is necessary to overcome cohesion in the hardened polymer. To achieve maximum adhesion, solids are joined in a plastic or elastic state under pressure, for example, when gluing with rubber cement or when cold welding metals. Strong adhesion is also achieved with the formation of a new solid phase at the interface, for example in the case of galvanic coatings, or with the formation of surface chemical compounds (oxide, sulfide and other films). Polymer adhesion occurs better if the macromolecules are polar and have a large number of chemically active functional groups. To improve adhesion, active additives are introduced into the adhesive or film-forming polymer, the molecules of which are firmly bonded to the film at one end and to the substrate at the other, forming an oriented adsorption layer. When two volumes of the same polymer come into contact, autohesion (self-adhesion) can occur, when there is diffusion of macromolecules or their sections from one volume to another. At the same time, the bond strength increases over time, tending to the limit - cohesive strength. The phenomenon of adhesion occurs during welding, soldering, tinning, gluing, in the production of photographic materials, as well as when applying paint and varnish polymer coatings that protect metal parts from corrosion; The reasons for adhesion failure in the latter case are stresses arising due to film shrinkage, as well as the difference in the thermal expansion coefficients of the film and metal. Adhesion is not only a condition for the formation of a high-quality coating, bonding weld or adhesive seam, but also causes increased wear of rubbing parts. To eliminate adhesion, a layer of lubricant is introduced to prevent contact of surfaces. According to TSB.